Kirchhoff modeling and migration in weakly anisotropic medium using the pWFC (perturbed WaveFront Construction method)

Abstract

The presence of velocity anisotropy in the layers or in the overburden leads to mispositioning of reflector structures and degradation the image quality, when an isotropic migration processing is performed on seismic data. These distortions occur even for weakly anisotropic layers, which are the most common type of rocks in geologic models for seismic applications. In this paper we present a method where a first-order perturbation is applied to the wavefront construction algorithm which generates a traveltime table that fits the traveltime of a weakly anisotropic medium with arbitrary of symmetry. We call this method the perturbed WaveFron Construction (pWFC). These traveltime tables are used in traditional Kirchhoff modeling and migration algorithm. The pWFC allows an approximated computation of traveltime tables for weakly anisotropic medium efficiently, avoiding a more intensive computation by a full anisotropic ray-tracing algorithm. To illustrate the difference when considering or not weak anisotropy in the seismic processing, two common-offset (100m and 1100m) data were modeled using WFC isotropic and using pWFC method. The 1100m dataset was migrated twice using a Kirchhoff algorithm once using an isotropic traveltime tables and the other a traveltime tables computed by the pWFC method.